Cv Valves Henry

ITER meeting Grenoble – June 14th & 15th 2005 [email protected] 1/11

Euratom

Calculationof

Kv – Cv coefficients

European standardsFor

Control valves sizing

Denis HENRY


EuratomOutlineOutline

General description of Cv coefficient

Valve flow characteristics

European standard for valve sizing

Conclusion


Euratom

In addition to the service conditions, the flow control valve specifications gathers the following characteristics :

- valve size (DN)- sort of valve (butterfly, rotatable, plug …)- plug profile- flow direction

General description (1)General description (1)

The valve flow capacity is defined by the value of the Cv coefficient which is applicable for any kind of fluid.

with the valve device, the manufacturer has to provide the technical data including :- Fd factor depending on the hydraulic diameter.- FL factor taking in account the choked flow due to cavitations phenomena.- XT factor taking in account the choked flow in case of critical pressure drop.- Cv coefficient (full opening or 80% opening)

For a defined fluid, the characteristic of a flow control valve is the pressure drop as function of the flow capacity for several stroke values.


EuratomGeneral description (2)General description (2)

Valve flow coefficients(liquid flow)

∆pρQAv ⋅=

Q (m3/s) Virtual cross section in m2 of volumetricρ (kg/m3) flow rate flowing through the valve ∆p (Pa) (use I.S. units)

Q (m3/h) Numerical value in m3/h of water at 15 °C (ρw)ρ (kg/m3) flowing through the valve at ∆pkv = 105 Pa ∆p (Pa)wρ

ρ⋅

∆⋅=

∆ppQK vk

v

Q (gal/min) US Numerical value in US gal/min of water at 15 °C (ρw)ρ (lb/ft3) flowing through the valve at ∆p = 1 psi ∆p (psi) (usually applied)wρ

ρ⋅⋅=

∆p1QCv

Conversion

1078.2KA 5

v

v −⋅= 1040.2CA 5

v

v −⋅= 1065.8CK 1

v

v −⋅=


EuratomGeneral description (3)General description (3)

valve flow characteristics

Digital(on/off)

Linear flow(lin.)

Equal percentage(=%)

Relative “Cv” = f (Relative opening “h”)

Interest for control system

( )hCC

fov

v f==Φ

Cv Current Cv value Cvfo Full opening Cv value h Relative opening %

Rangeability

0v

v0

1CCR

mo

fo

Φ==

Cvfo Full opening Cv valueCvmo Minimal opening Cv value Φ0 Maximum relative Cv


EuratomValve flow characteristicsValve flow characteristics

Linear flow

hm0 ⋅+Φ=Φ

01m Φ−=

00

1RΦ

=With the slope

And the rangeability

gives1R1-.Rh

0

0

−Φ

=

h (%) Valve stroke

Relative Cv

Equal percentage

hn0

⋅⋅Φ=Φ e

⎟⎠⎞

⎜⎝⎛Φ

=0

1lnnWith

And the rangeability

gives( )( )00

Rln.Rlnh Φ

=

h (%) Valve stroke

Relative Cv

00

1RΦ

=


EuratomEU Standards for valve sizing (1)EU Standards for valve sizing (1)

Two-phase flow

No generally acceptedstandard method exists.

All described methods include a lot of

uncertainty

Single-phase flow

Liquid Service Gas/Vapour Service

Taking into account of

- thermophysical properties of fluid

- plug profile of the valve

- piping geometry (including convergent/divergent devices)

- Reynolds’ numbers

Standards’ references

Industrial-process control valves. Part 2-3 : flow capacity. Test procedures.

NF EN 60534-2-3

Industrial-process control valves. Part 2-1 : flow capacity. Sizing equations for fluid flow under installed conditions.

NF EN 60534-2-1

Industrial-process control valves. Part 1 : terminology of the valves of regulation and general considerations

NF EN 60534-1



NF EN 60534 2-1



1.5 kg/s

13.5 kPa

2 kPa 2 kPa

PID ACB_TF

CV 719Φ :DN 80Tin : 4.6 KPin :395 kPaPout :381.5 kPaQm :3 kg/sCv :95


EuratomConclusionsConclusions

The main supplier of flow control valve like VEKA or VELAN use their own code which refers to EU standards.

In the frame of EFDA tasks concerning the the design of the ITER cryodistribution, the valve sizing are performed according to the EU standards.

CEA implemented an Excel-macro for the Cv calculation in accordance with the EU standards.

A comparison of several Cv values will be carried between those given by the suppliers and the results of CEA calculations.

Cv Valves Henry

Documents

Transcript of Cv Valves Henry